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High Energy Physics - Phenomenology

Abstract: We revisit the issue of color neutrality in effective model descriptions of
dense quark matter based on global color symmetry. While the equilibrium
thermodynamics of such models is now well understood, we examine the collective
modes, focusing on the fluctuations of the order parameter. We point out that
the constraint of color neutrality must be carefully generalized in order to
obtain physically consistent and well-defined results. Particularly important
is that the collective modes associated with order parameter fluctuations
couple to charge density fluctuations in the neutral medium. We start by
proving explicitly that, in contrast to claims made previously in literature,
Nambu-Goldstone bosons of spontaneously broken global color symmetry remain
exactly massless even after imposing the color neutrality constraint. As the
next step, we make the argument general by using effective field theory. We
then employ the high-density approximation to calculate the couplings in the
effective Lagrangian and thus the Nambu-Goldstone boson dispersion relations.